This invention relates to a method for rhinostereometric measurement as well as a device for implementing the method, comprising optical equipment for determining the coordinates of one or more points on a person's nasal mucosa.
Rhinostereometry is a known optical method used for measuring the congestion of the nasal mucosa. The head of the person to be subjected to such measuring is fixed in a coordinate system. The positions in the coordinate system of a number of points on the nasal mucosa are then determined with the aid of a surgical microscope placed on a micrometer table so as to be movable in all three dimensions. Rhinostereometry is described in more detail in a doctoral thesis by Jan-Erik Juto: Rhinostereometry, Stockholm, 1985, ISBN-91-7222-905-5.
In order that the results of rhinostereometric measurements should be comparable, the head of the test subject must occupy exactly the same position in the coordinate system every time. Positional accuracy has to be extremely high, since a point on the nasal mucosa moves about 4 mm at the most when the mucosa changes from a state of minimum congestion to one of maximum congestion. Such accuracy is hard to achieve.
The object of the invention is to provide a method and a device making it possible to obtain comparable results in rhinostereometric measurements performed on different occasions.
This object is achieved by a method having the distinctive features recited in appended claim 1 and by a device having the distinctive features recited in appended claim 6. Preferred embodiments of the invention are defined in the appended subclaims.
Because the position of a person's face in the coordinate system is determined on each measuring occasion and is then transposed to a reference position in the coordinate system, comparable results can be obtained on different measuring occasions regardless of the position of the face in the coordinate system by a corresponding transposition of the coordinates of the measured point on the nasal mucosa. In this way, the person's head need not be fixed in exactly the same position on all measuring occasions, but the head may change positions between them.
Preferably, the position of a person's face is determined by contactless distance measurement from fixed locations in the coordinate system, e.g. by means of radar, ultrasound or laser. At present, laser is preferred for reasons of accuracy. Also the coordinates of a point on the person's nasal mucosa are advantageously determined by laser instead of a surgical microscope.
To increase the accuracy of the positional determination, the movements of the person's head are advantageously restricted by mechanical fixing means, e.g. in the form of a spectacle frame.